1. Field of the Invention
The present invention relates to a vehicle lamp fabricated by fitting a bulb as a light source into a bulb fitting hole provided in a lamp body by bayonet engagement, and fitting an annular gasket in between a flange portion provided on the periphery of a bulb socket and the peripheral edge portion of the bulb fitting hole whereby to seal the bulb fitting hole, and more particularly to a vehicle lamp having a lamp body and a front lens which are integrally formed by blow molding.
2. Related Art
In order to decrease the number of parts constituting a lamp, a conventional vehicle lamp is constructed as shown in FIG. 11 through the steps of integrally forming a lamp body portion 2 and a front lens portion 3 by blow molding into a hollow body lens unit 1, fitting a bulb 5 as a light source into a bulb fitting hole 4 formed in the lamp body portion 2 of the body lens unit 1 by bayonet engagement and fitting an annular gasket 7 in between a flange portion 6a provided on the periphery of a bulb socket 6 and the peripheral edge portion 4a of the bulb fitting hole whereby to seal the bulb fitting hole 4.
The gasket 7 has a transverse cross section so that its wall thickness is gradually reduced toward the inner peripheral side so as to make easy the mounting of the gasket on the bulb socket 6.
In the case of such a conventional lamp, however, since the body lens unit 1 essentially consisting of the lamp body portion 2 and the front lens portion 3 is formed by blow molding, the wall thickness of the peripheral edge portion 4a of the bulb fitting hole varies in the peripheral direction, and the annular gasket 7 protrudes from the flange portion 6a at the time the bulb 5 is fitted into the bulb fitting hole 4, thus posing a problem arising from insufficient waterproofing.
More specifically, as the hollow body lens unit 1 is formed by blow molding through the steps of supplying compressed air into a plastic parison to make the plastic material follow the molding surface by expanding the parison, there develops a variation in plate thickness (hereinafter called a deviation) between regions where the plastic material greatly expands and does not so much and such a plate thickness deviation becomes conspicuous in the lamp body portion 2 which is greatly expanded in particular. In other words, plate thicknesses ti and t2 in the peripheral edge portion 4a of the bulb fitting hole 4 provided in the lamp body portion 2 differ from each other in the peripheral direction (t1&lt;t2).
When the bulb 5 is fitted into the bulb fitting hole 4, furthermore, the presence of the plate thickness deviation makes compressive force acting on the gasket 7 on the thin-walled plate side smaller than what acts thereon on the thick-walled plate side, though compressive force acting thereon in the peripheral direction in any region remains constant when the plate thickness deviation is absent in the peripheral edge portion 4a of the bulb fitting hole 4. Since the transverse cross section of the gasket 7 is such that the wall thickness of the gasket 7 is gradually reduced toward the inner peripheral side, the compressive force causes the gasket 7 on the thick-walled plate side to protrude in particular, which results in insufficient waterproofing.